1. Field of the Invention
This invention relates to high strength, high rigidity polyamide composition having less reduction of physical properties at high humidity environments, to be used for mechanical and electric parts including inertial mass such as flywheel or micromotor parts, and also relates to a polyamide composition especially suitable for automobile underhood parts having resistance to calcium chloride and zinc chloride employed as antifreeze of road surface.
2. Prior Art
Plastic replacement of automobile parts are extensively examined because it contributes to reducing the weights of automobile. Since polyamide resin is superior in heat resistance, mechanical properties, chemical resistance, oil resistance, moldabilities, etc., it is examined and being used for wide application in automobile parts.
But, since the strength and rigidity of polyamide, having rich amide group such as nylon 6, nylon 66, and nylon 46 largely changes between dry and wet condition so it is very unstable in physical properties and dimensional stability, they also have a serious defect that since they have affinity with metal ions, they are attacked by chlorides such as calcium chloride or zinc chloride, so it extremely difficult to the application for automobile underhood parts such as fuel tubing, intake manifold pipe, clutch master cylinder, motor washer, fastener grip, lamp socket, relay block for switches, connector, etc.
Many attempts have been made to solve the problems including, addition of hydrocarbon groups of 6-22 carbon numbers, blending polyolefin with polyamide, blending polyolefin polymer having acid anhydride at the chain end, blending ethylenic ionomer and/or nitril rubber to nylon, blending lower amide group polyamide, blending polyamide having aromatic constituent, but these attempts cannot improve resistance competitive to nylon 12 or nylon 11.
But nylon 12 and nylon 11 have lower heat resistance than nylon 6 and are very high cost plastics, a cheaper material having resistance to chlorides have eagerly desired by the industries.
As a prior art for a plastic for automobile underhood parts, Japan Patent S62-9617 (Reference 1) proposes a two components resin compound (A+B) wherein (A) 25-95 weight % of aliphatic polyamide and (B) 5-75 weight % of amorphous polyamide mainly composed of aromatic amino acid and/or aromatic discarboxylic acid.
The aliphatic polyamide of component (A) are, by the detailed description of the reference 1, polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecanamide (nylon 612), polyundecanoamide (nylon 11), polydodecanamide (nylon 12) and their copolyamide, mixed polyamide. The degree of polymerization is not specified, and polyamides having relative viscosities in the range of 2.0-5.0 can be selected.
Then the amorphous polyamide, mainly composed of aromatic amino acid and/or aromatic dicarboxylic acid of component (B) are, the polyamide made by melt polymerization of aromatic amino acid and/or aromatic dicarboxylic acid such as p-aminomethyl benzoic acid, p-aminoethyl benzoic acid, m-aminomethyl benzoic acid, terephthalic acid, isophthalic acid, etc.
It is described that hexamethylene diamine, undecamethylene diamine, dodecamethylene diamine, 2.2.4-/2.2.4-trimethylhaxamethylene diamine, m-xylilene diamine, p-xylilene diamine, p-aminocyclohexyl methane, p-aminocyclohexyl propane, bis(3-methy,4-aminocyclohexyl) methane, 1.3-bis(aminomethyl) cyclohexane, 1.4-bis(aminomethyl) cyclohexane, isophorondiamine, etc. can be used as the diamine for another component of polyamide. But there are no description on the effect for the resistance for zinc chloride which exhibit the most severe action among many chlorides.
Opened Patent H4-23863 (Reference 2) proposes polyamide composite for the parts of mechanical, electric and automobile use, improved in rigidity and strength by addition of inorganic fibers (F) such as glass fibers, carbon fibers, etc. to the melt blend of (A) component of Reference 1 and semiaromatic amorphous polyamide (hereinafter referred to as component (C)).
The said (C) component is a polymeric material having molecular structure of linking main chain units of linear aliphatic hydrocarbon and aromatic hydrocarbon by amide group, and is essentially amorphous transparent polyamide and copolyamide. But there is no description about the special effect for the resistance for chlorides.
Contrary to prior arts described above which are only based on the viewpoint of diluting the amide groups in the polyamide molecular chain or reducing the water absorption, this inventor had concentrated his energy to the polyamide composition for improving the resistance to chlorides, and finally developed a composition of this invention characterized in having superior strength and rigidity and also possesses resistance to chlorides, thus completed the present invention as described below.